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Zero-kinetic-energy (ZEKE) photoelectron spectroscopy was used to probe the vibrational levels in the ground electronic state of the chlorobenzene cation using a two-color photoionization scheme via the $S1$ electronic state of the $neutrala$. Exciting through different $S1$ vibrational levels has revealed mixing of some $S1$ normal coordinates in the ground state of the cation. A previously-identified Fermi resonance in the $S1$ state of the neutral is also confirmed by the ZEKE spectra. The adiabatic ionization energy is measured as $73170\pm 5cm-1$.